I declined my manager invitation?

Honestly, I don't understand why everyone carries on about how you should go to something if your boss invites you - if you don't want to go, you don't have to and you don't owe anyone an explanation. If someone asks why you weren't there, just say that you already had plans. They don't need to know whether those plans were to simply sit around at home watching television or not. I don't really think it will look bad if you don't go - we can't all be free at the same time and people need to understand this. If your boss regularly invites you to dinner, however, I wouldn't make it a habit to decline - this WILL make you look bad and as if you're avoiding spending any time with him. In this case, I would accept the next invitation.

There is no reason that you need to socialize with the boss, unless he holds it against you. Maybe you need another job. or just don't over think this stuff.

Just have confidence in who you are and you don't owe any one an explanation. If they are rude and push for an answer, then tell them that you had other plans, and if they ask what plans, give a vague answer or say it was a family thing or tell them that you had a personal reason,

Some jobs have a social structure that you might have to fit in to. only you can make that call.

Only you can know your reason for not attending this dinner so be honest and simply advise them as such. You then need to decide what you tell your co-workers and your boss if they ask why you did not attend the dinner.

Say you were sick, and that you will have a doctor's note for them- if needed.

If your boss invites you to his home, you go.

Yes, you will look bad if you don't go.

Just say you had some family affair that you could not get out of.